The invention pertains to a wire electrode arrangement for electroerosive cutting and a method for implementing said arrangement. The method of electroerosive cutting utilizes the effect of a potential difference between the electrode and a conductive workpiece to be processed. This potential difference causes spark discharges that, in turn, lead to the removal of material from the workpiece to be processed. Such methods are known from the state of the art.
In conventional methods for cutting by means of electrical discharge machining, the electrode consists of only one wire which is conductive throughout its cross section. The cutting speed is limited by the number of discharges per time unit and the energy of each discharge (i.e., the maximum current density) because local overheating of the wire can lead to wire breakage.
Various patents, e.g., U.S. Pat. No. 5,196,665 or U.S. Pat. No. 4,740,666, describe methods in which the electrically conductive core of a wire which consists of an alloy is coated with one or more layers of different materials. These materials preferably consist of metals with low melting and evaporating temperatures and superior electrical conductivity, e.g., zinc. Consequently, it is possible to attain a wire core with high tensile strength which is additionally protected from possible wire breakage by the coating that acts as a heat shield. Such a wire electrode makes it possible to operate with high current densities and consequently increase the machining speed. According to F. Dauw (ISEM-X) these measures made it possible to double the cutting speed (between 1986 and 1990). However, an additional increase in the cutting speed can hardly be attained by exclusively utilizing one of the above-mentioned methods.
Another method for increasing the machining speed which is known from the field of electroerosive cavity sinking simultaneously utilizes several electrodes. Consequently, it is possible for discharges to occur at different positions per time unit. The utilization of several electrodes for electroerosive cutting was described in EP 0,433,747. However, the objective of this publication pertains to the cutting of nonconductive materials. In this case, the cathode as well as the anode are situated on a wire-shaped arrangement such that discharges occur between the electrodes of the wire arrangement, but not between the wire arrangement and the workpiece. Consequently, the geometry of this arrangement is not suitable for the desired type of machining, i.e., several simultaneous discharges are not possible.